Combine the chocolate chips, egg, and vanilla in a blender. Process on pulse mode until the chocolate is chopped. In a small pan over medium heat, heat the heavy cream, stirring frequently, until small bubbles just begin to appear. Do not let it boil. With the blender running, carefully pour the heated cream through the feed tube of the blender cap and process until the chocolate is melted and the mousse is smooth, about 60 seconds. Divide the mousse between individual serving dishes. Cover with plastic wrap and place in the refrigerator for 2-3 hours or until completely chilled. Serve, topped with whipped cream, if desired.